To obtain information on the primary and tertiary structure of the antibody combining region. We have attempted to find out whether a single combining region bound only a single antigenic determinant or a family of structurally related determinants at a single binding site, or whether the combining region on a single immunoglobulin is a mosaic consisting of sub-sites at which a number of structurally diverse haptens may be bound ("multiple binding" combining regions). If multiple binding combining regions exist, are they also "polyfunctional"? If several antigenic determinants bind to one immunoglobulin, is each of these determinants capable of inducing the production of the immunoglobulin which bind these determinants? To study the biological and genetic consequences of "polyfunctional" binding regions.